Process of evaporating liquids and apparatus for carrying out the same



May 16, 1944. PLACEK PROCESS OF EVAPORATING LIQUIDS AND APPARATUS FOR CARRYING OUT THE SAME Flled July 23, 1940 M Md 1 47% I N "1 M3? hwl W045.

Patented May 16, 1944 PROCESS OF EVAPORATING LIQUIDS AND APPARATUS FOR CARRYING OUT THE SAME (Adolph Placek, Philadelphia, Pa. AIIDIiCatiOn 23, 1949, Serial N0. 347,006

6 Claims.

The invention relates to new and useful. improvements in a process of concentrating liquids by evaporation and the apparatus for eff ciently carrying out said process.

An object of the invention is to provide a proc ess wherein the liquid to be concentrated is caused to flow by centrifugal force from an established axis of introduction in all radial directions therefrom, and wherein said flowing liquid has imparted thereto a high velocity of rotational movement about said axis, and wherein said liquid rotating at high velocity is caused to move at substantially the same velocity along a stationary cylindrical heating surface which is located concentrically with reference to said axis.

Another object of the invention is to provide a process of the above type whereby vapors of low boiling constituents of said liquid may be separately withdrawn from the vapor space adjoining said axis of liquid introduction, and vapors of high boiling constituents of said liquid are withdrawn from the vapor space adjoining the stationary heating surface.

A further object of the invention is to provide an apparatus which is simple in construction and which provides for the continuous flow of liquid to be vaporized from an axially located liquid feed distributing device in all radial directions, and wherein said radially flowing liquid has imparted thereto a high velocity of rotational movement and is subsequently forced to flow at a high velocity along a stationary cylindrical heating surface which is located concentrically with reference to the axis of rotation of the liquid.

Another object of the invention is to provide an apparatus of the above type which includes a rotating impeller provided with means at or near the center thereof for receiving the liquid to be vaporized, and wherein said impeller conveys and uniformly distributes said liquid in all radial directions and tangentially discharges said liquid at its periphery and at substantially the same velocity along a stationary cylindrical heating surface which is located close to and concentrically with reference to the periphery of said rotating impeller.

Still another object of the invention is to provide an apparatus consisting of a stationary casing having side walls and a cylindrical wall which constitutes the heating surface wherein one or both side walls of said casing are provided with an outlet or outlets for the evaporated vapor, which casing houses a concentrically located impeller receiving the liquid centrally thereof spaced parallel circular plates 3, 4, 5 and 6.

and causing the liquid to flow by centrifugal force generated by rapid rotation of the impeller in all radial directions to the periphery of the impeller from which it is discharged tangentially in a uniformly distributed form substantially with the peripheral velocity of said impeller along the stationary heating surface.

These and other objects will in part be obvious and will in part be hereinafter more fully disclosed.

In the drawing which illustrates an apparatus for carrying out the inventions- Figure 1 is a vertical sectional view through an apparatus embodying the improvements, said section being taken through the axis of rotation of the impeller;

Fig. 2 is a sectional view on the Figure 1, and

Fig. 3 is a view similar to Figure 1, but showing a silghtly modified form of means for removing the vapors of evaporation from the apparatus.

An apparatus has been devised for carrying out my process which is very simple in construction. It will be understood, however, that the process may be carried out on anapparatus differing widely in detail from that illustrated. The illustrated apparatus will be described in detail, and then the process will be described by reference to the apparatus.

The apparatus includes a stationary cylindrical casing l in which is journaled a rotatable impeller 2. The impeller consists of a plurality of All of these plates are provided with identical circumferential and concentrical corrugations and so parallelly distanced that in radial cross section the spacings between said plates show identical and sinuous passageways through which liquid flowing radially from the center of the impeller to its periphery must impact each corrugation preferably at one-half to one-third of its amplitude. By progressive impacts and radial flows of liquid from one corrugation to another due to a friction between the liquid and the surfaces of the plates, the said liquid is gradually imparted with an increasing velocity and finally leaves the periphery of the impeller in tangential directions substantially with the same velocity as the peripheral velocity of the impeller. The said corrugated plates maybe solid or perforated, if a greater degree of mixing or distribution of liquid is desired. The plates are assembled together by means of bolts 1, 1 and spaced uniformly from each other by means of spacing blocks 8, 8 which are placed around the bolts between each plate.

line 2-2 of Bolts 1, I extend through all of the plates and are firmly tightened by nuts 9, 9 with an external frame. Other means, of course, may be used for assembling and spacing the plates of the impeller. However, it is desirable that the plates shall be uniformly spaced and that there shall be a free and uniform passage between the plates from the center of the impeller to its outer periphery. The plate 3 constituting one wall of the impeller is rigidly secured to a shaft Ill which passes through a stufiing box I I in the stationary side wall of the casing and is mounted in bearings l2, l2 in a suitable frame. -There are two spaced bearings, and these serve to support the shaft so that it will rotate about a fixed axis. Between the bearings l2, I2 is a pulley l3 by which the shaft may be driven. The wall 6 has an opening at the center through which is installed a stationary pipe I4, which pipe enters the apparatus through the side wall of the easing, to which it is rigidly and tightly fixed and extends to the center of the impeller and serves as a means for delivering the liquid to be evaporated. Said pipe is provided with a series of perforations l so arranged that the liquid will be uniformly distributed to each passageway of the impeller.

The flow of the liquid to-the apparatus may be controlled by a valve IS. The cylindrical wall of the casing is the heating surface l1. This surface may be heated directly from the outside by fire, electrical means, or hot fluids like steam. The drawing shows a heating Surface provided with a jacket [8 into which the heating fluid medium is introduced through a valve l9 and discharged through an opening 20. The concentrated liquid is discharged from the apparatus through an opening 2| in the heating surface, and the vapors generated by evaporation of the liquid are withdrawn from the apparatus through an opening 22 suitably provided in the side wall of the casing.

The process embodying the invention will be best understood by the description of the operation of the apparatus. The impeller is rotated at a high velocity. The'liquid to be vaporized is passed into the apparatus through the stationary pipe l4 and is uniformly distributed to the central part of the impeller. The centrifugal force incident to the rapid rotation of the impeller causes the liquid to spread and to flow in all radial directions toward the outer periphery of the impeller. While flowing in all radial directions, said liquid successively impacts the walls of the passageways in the impeller, and due to the friction which exists between said walls and liquid, the rotational velocity of said liqu d is gradually accelerated and finally the said liquid leaves the periphery of the impeller in tangential directions substantially imparted with the same velocity as the peripheral velocity of the impeller. The stationary cylindrical heating surface is very closely and concentrically located with reference to the circumferential periphery of the impeller. Q

Consequently, the liquid issuing tangentially in all directions from the periphery of the impeller impinges the heating surface at a very sharp angle, so that the velocity of liquid along the heating surface is only slightly reduced, due to the impingements and due to the inherent friction between the liquid and the heating surface. The minimum tolerable clearance between the periphery of the impeller and the heating surface is only limited by the minimal space along the heating surface, which is required for the escape of vapor generated on said heating surface.

It is a well known fact that the film coefficient of heat transfer from heated surfaces to liquids and consequently the rate of heating and of evaporation is a function of the velocity of liquid, with which it moves along the heating surface.

In previous arts, high velocities of liquid to be heated or evaporated along a heating surface have been attained by mechanical mixing, forced circulation by pumps, pumping effect of vapor expanding through long and narrow heating tubes, or simply by gravity flow over inclined heated surfaces.

The advantage of my process and apparatus is that, due to an enormous liquid velocity and consequently a high coefficient of heat transfer, a comparatively small heater or evaporator with a small heating surface can perform much more than any apparatus of same size employed heretofore.

In actual practice, it is usually estimated that the liquid film coefficient increases with 0.6 to 0.8th power of velocity of liquid along a heated surface.

Since the velocity of tangentially projecting liquid spray from the periphery of the impeller substantially equals to the length of periphery of the impeller, times the number of revolutions per second, it is easily conceived what an enormous velocity can be imparted to the liquid by said impeller. Thus if the diameter of the impeller is only one foot and the revolutions of the impeller 6000 R. P. M., or one hundred per second, the velocity of the liquid projected tangentially against a stationary cylindrical heating surface, which is located concentrically with reference to the periphery of the impeller, would substantially be 1 X 3.14 X :314 feet per second Another advantage of my invention is that the liquid moves along the heating surface in the form of a very thin layer, such that the hydrostatic head of said liquid over the heating surface is negligible. Therefore, the lost degrees in temperature difference, due to hydrostatic head, are also negligible, and consequently a much greater heat transfer is effected than as compared with usual types of evaporators having the same heating surface and operating under the same apparent temperature difference.

Another advantage of my invention is that, due to centrifugal force to which the liquid and the evolved vapor are subjected, entrainment and foaming of liquid is completely eliminated.

Still a further advantage of my invention is that the liquid to be treated stays in the process only a fraction of a minute, and therefore, where liquids or solutions are very susceptible to a prolonged heat exposure, my invention functions very successfully.

Although the drawing shows my preferential type of impeller, the spirit of my invention will not be aifected, if any other type of impeller is employed in practicing my process, provided this impeller distributes the liquid uniformly in all radial directions and tangentially projects a uniform liquid spray substantially with a velocity of the periphery of the impeller against a cylindrical heating surface, which is very closely and concentrically located with reference to the periphery of said impeller.

Figures 1 and 2 show an apparatus which functions as a heater and evaporates only,

wherein the vapors evolved on the heating surface may be withdrawn at any convenient point of one 'of'the stationary sides of the'casing, and wherein the impeller only acts as a distributing and velocity imparting means for the liquid.

In many processes the liquid to be evaporated Contains lower boiling constituents, which must be distilled oif and separately recovered from the vapor of higher-boiling constituents of the liquid.

For this purpose, my process and apparatus may be modified to meet such requirements.

Figure 3 shows by way of example, a vertical section through such a modified apparatus.

This apparatus is similarly built as that illustrated in Figures 1 and 2, excepting the following modifications:

The wall 6 of the impeller has a centrally located opening through which said wall is rigidly and tightly connected to a hollow shaft 23. This hollow shaft passing through a stufiing box 24 in the stationary side of the casing is connected to a stationary vapor take-off pipe 25 by means of an elbow 26 rigidly adapted to the stuffing box 24. The liquid inlet pipe I4 is extended to the center of the impeller through the hollow shaft from the elbow 26. The vapor take-off pipe is provided with a controlling valve 21, and the vapor take-01f opening 22 is provided with a controlling valve 28.

While operating the apparatus shown in Figure 3, by opening the valve 28 and closing the valve 21, the vapors evolved on the heating surface may be entirely withdrawn from the apparatus through the opening 22, or by closing the valve 28 and operating the valve 21, the vapors evolved on the heating surface flow in countercurrent to the liquid through the impeller and are withdrawn at the center of the impeller through the hollow shaft 23. In this latter case, the impeller functions not only as a distributing and velocity imparting means for the liquid, but it also functions as a liquid pre-heating and fractionally distilling means for vapors of the lower-boiling constituents of the liquid.

In practicing the process of evaporation in the above-described apparatus, my method consists in appropriately regulating the withdrawal of vapors generated on the heating surface, whereby one portion; of said vapors, being led in counter-current to the introduced liquid through the impeller, causes to distill off vapors of lowboiling constituents of said liquid, which vapors are withdrawn at the center of said impeller, and whereby the other portion of vapors generated on the heating surface is withdrawn from the casing of the apparatus.

This regulation of withdrawal of vapors from the apparatus is accomplished by appropriately adjusting the flow through the controlling valves 27 and 28.

While I have shown in the drawing the impeller as rotating about a horizontal axis, it will be understood that the axis may be vertical or otherwise arranged without affecting the operation of the apparatus and the carrying out of the process.

It is obvious that many changes in the details of construction of the apparatus may be made without departing from the spirit of the invention as set forth in the appended claims, and that the process may be carried out in other forms of apparatus than in the one illustrated.

Having thus described the invention, what I claimas new and desire to secure by- Letters Patent is:

' l. The process of concentrating liquids by evaporation consisting in forcing the liquid outwardly from or near an established axis at the center of a cylindrical heating surface through a radially sinuous passage of substantially uniform width, while rotating the passage to exert centrifugal force on the liquid for causing the same to move in all radial directions outwardly at an increasing velocity, said liquid when discharged from said passage being caused to contact with and move along the heated surface atsubsta-ntially the same velocity as the'peripheral velocity of said passage.

2. The process of concentrating liquids by evaporation consisting in forcing the liquid outwardly from or near an established axis at the center of a cylindrical heating surface through a plurality of radially sinuous passages of substantially uniform width, while rotating the passages to exert centrifugal force on the liquid for causing the same to move in all radial directions outwardly at a high velocity, said liquid when discharged from said passages being caused to contact with and move along the heated surface at substantially the same high velocity, and withdrawing the concentrated liquid from said heating surface and withdrawing the vapors at a point nearer the axis of rotation.

8. An apparatus for concentrating liquids by evaporation comprising a stationary casing havingan inner heated cylindrical surface, an impeller rotating about an axis at the center of said cylindrical heating surface, said impeller including uniformly spaced plates shaped so as to form sinuous passages, means for discharging the liquid to be concentrated on to said plates whereby the liquid is caused by centrifugal force to flow outwardly on said plates in all radial directions and at a rapidly increasing velocity, the periphery of the impeller being close to the cylindrical surface whereby the liquid discharged tangentially from the impeller will be caused to move along the heated surface at substantially its maximum velocity.

4. An apparatus for concentrating liquids by evaporation comprising a stationary casing having an inner heated cylindrical surface, an impeller rotating about an axis at the center of said cylindrical heating surface, means for discharging the liquid to be concentrated on to said impeller whereby the liquid is caused by centrifugal force to flow outwardly thereon in all radial directions and at a rapidly increasing velocity, the periphery of said impeller being close to the cylindrical surface whereby the liquid discharged tangentially from the impeller will contact with and move along the heated surface at substantially its maximum velocity, said cylindrical surface having an outlet for the concentrated liquid, said casing having an outlet for the vapors disposed between said cylindrical surface and the axis of rotation of the impeller.

5. An apparatus for concentrating liquids by evaporation comprising a stationary casing having an inner heated cylindrical surface, an impeller rotating about an axis at the center of said cylindrical heating surface, means for discharging the liquid to be concentrated on to said impeller whereby the liquid is caused by centrifugal force to flow outwardly thereon in all radial directions and at a rapidly increasing velocity, the periphery of said impeller being close to the cylindrical surface whereby the liquid discharged tangentially from the impeller will contact with and move along the heated surface at substantially its maximum velocity, said cylindrical surface having an outlet for the concentrated liquid, said casing having a valve-controlled outlet for vapors disposed intermediate the cylindrical surface and the axis of the impeller, and a valveoontrolled outlet for vapors at the axis of the impeller.

6. An apparatus for concentrating liquids by evaporation comprising a stationary casing having a cylindrical surface, means for heating said cylindrical surface, an impeller rotating about an axis at the center of said cylindrical heating surface, said impeller including a plurality of uniformly spaced corrugated plates providing sinuous passages, means located at the axis of said impeller for discharging the liquid to be concentrated on to said plates whereby the liquid is caused by centrifugal force to flow outwardly on to said plates in all radial directions at a rapidly increasing velocity, the periphery of said impeller being close to the cylindrical surface whereby the liquid discharged tangentially from the impeller will be caused to move along the heated surface at substantially vits maximum velocity, means connected with said cylindrical surface for withdrawing the concentrated'liquid therefrom at a low point of said cylindrical surface, and means connected with the casing for withdrawing the vapor from the casing at a point .16 radially within the cylindrical surface.

ADOLPH PLACEK. 

